The present invention relates to a novel fluorine-containing unsaturated cyclic compound, a novel fluorine-containing polymer having an aliphatic monocyclic structure in its trunk chain, and a chemically amplifying photoresist composition which is obtained from the fluorine-containing polymer, is excellent in transparency and possesses improved dry etching resistance.
As a result of an increasing necessity for high integration of a large scale integrated circuit (LSI), microfabrication technology is required for photolithography. In order to satisfy such requirements, there have been tried to use, as exposure light sources, a deep ultraviolet, a KrF excimer laser beam (wavelength: 248 nm) and a ArF excimer laser beam (wavelength: 193 nm) which have a wavelength shorter than conventional g-rays (wavelength: 436 nm) and i-rays (wavelength: 365 nm). Those light sources are put into practical use.
Recently a process using a F2 laser beam (wavelength: 157 nm) having a wavelength in a vacuum ultraviolet region has been studied in an ultra-microfabrication technology and is considered promising as an exposure technology aiming at a technology node of 0.1 μm.
On the other hand, in the pattern formation, a chemically amplifying resist which becomes advantageous in transparency, resolution, sensitivity and dry etching resistance in cases of energy rays having various wavelengths has been studied. The chemically amplifying resist means, for example, in case of a positive resist, an energy-sensitive composition comprising a resin being soluble in an alkali developing solution and having an introduced substituent which has an effect of inhibiting dissolution of the resin but is deprotected due to action of an acid, and a compound which generates an acid by irradiation of energy rays such as light and electron beam (hereinafter referred to as a photoacid generator). When the composition is irradiated with light or electron beam, an acid is generated from the photoacid generator, and by heating (post-exposure bake, which may be hereinafter referred to as “PEB”) after the exposure to light, the substituent which has been giving a dissolution inhibiting effect on the resin is deprotected due to action of an acid. As a result, the exposed portion becomes soluble in alkali, and by treating the exposed portion with an alkali developing solution, a positive resist pattern can be obtained. In that case, the acid acts as a catalyst and exhibits its effect in a very small amount. Also action of the acid becomes active by the PEB and a chemical reaction is accelerated like a chain reaction, and thus sensitivity is enhanced.
Examples of conventional resins for chemically amplifying resist are phenol resins in which a part or the whole of hydroxyl is protected by a protective group such as acetal or ketal (KrF resist), methacrylic acid resins in which an acid-labile ester group is introduced to carboxyl (ArF resist) and the like.
However those conventional resist polymers have strong absorption in a wavelength range of a vacuum ultraviolet region and have a significant problem that transparency against F2 laser beam having a wavelength of 157 nm which is studied in a process for ultra fine pattern is low (an absorption coefficient is high). Therefore for exposing with F2 laser, it is necessary to make a resist film thickness very thin and it is substantially difficult to use the polymers as a single layer F2 resist.
R. R. Kunz, T. M. Bloomstein, et al. suggest in Journal of Photopolymer Science and Technology (Vol. 12, No. 4 (1999) 561-569) that fluorocarbons have good transparency at 157 nm as compared with other various materials and have possibility of use as a F2 resist.
However in that literature, there is only description that existing fluorocarbon polymers are high in transparency at 157 nm, but there is no description as to preferable structure of fluorine-containing polymers. Also, for example, with respect to a fluorine-containing polymer having functional group necessary for a positive type or negative type chemically amplifying resist, neither evaluation of transparency nor synthesis of the polymer was made. Moreover the literature does not suggest a fluorine-containing base polymer material being preferable as a chemically amplifying resist and a preferable resist composition obtained therefrom at all, and there is found no possibility of forming a F2 resist pattern by using a fluorine-containing polymer.
Thereafter A. E. Feiring, et al. of E.I. du Pont de Nemours and Company disclosed in WO00/17712 pamphlet (published Mar. 30, 2000) that a specific fluorine-containing polymer is useful for F2 resist application.
That pamphlet describes the use of a fluorine-containing polymer having a structural unit of fluoroolefin and a structural unit having a polycyclic condensed structure which is mainly a structural unit derived from norbornene.
Also an acid-labile (acid-decomposable) functional group necessary for a positive type resist is introduced to the fluorine-containing polymer by copolymerizing a conventional acrylic, methacrylic, norbornene or vinyl ester monomer with a monomer having an introduced acid-labile (acid-decomposable) functional group.
Further thereafter A. E. Feiring, et al. of E.I. du Pont de Nemours and Company disclosed in WO00/67072 pamphlet (published Nov. 9, 2000) that a fluorine-containing polymer having —C(Rf)(Rf′)OH or —C(Rf)(Rf′)O—Rb is useful for F2 resist application.
In that pamphlet, a structural unit of norbornene in which —C(Rf)(Rf′)OH or —C(Rf)(Rf′)O—Rb is bonded through a part of —CH2OCH2— is disclosed. Further there is disclosed norbornene derivatives having —C(Rf)(Rf′)OH or —C(Rf)(Rf′)O—Rb as an example of a fluorine-containing polymer to be used for a resist.
However in those patent publications, there is no description as to the use of a fluorine-containing copolymer comprising a structural unit of fluoroolefin and a structural unit having an aliphatic monocyclic structure in its trunk chain, and further there is no description as to an aliphatic monocyclic structure to which a functional group necessary for a resist is introduced.
Further Katsuyama, et al. of Matsushita Electric Industrial Co., Ltd. proposed a method of forming a pattern with exposure light having a wavelength of from 1 to 180 nm using a resist material containing halogen atom, etc. (JP2000-321774A published Nov. 24, 2000). However there is disclosed only a methacrylic resin having a structural unit of methacrylic acid ester having —CH2CF3 group and —CH(CF3)2 group in its side chain as a base resin having halogen atom for a resist, and neither a resin containing fluorine atom in its trunk chain nor a polymer having an aliphatic monocyclic structure in its trunk chain is disclosed. Also there is disclosed no polymer which has, in an aliphatic monocyclic structure, a functional group and is capable of working as a chemically amplifying resist (positive type or negative type).
There is generally known that dry etching resistance of a polymer is enhanced by introducing a norbornene backbone to the polymer. However transparency, particularly transparency in a vacuum ultraviolet region of conventional norbornene derivatives cannot be said to be sufficient.
The present inventors have found that fluoroolefins represented by tetrafluoroethylene have good copolymerizability with unsaturated compounds (monomers) of aliphatic monocyclic structure, and a novel fluorine-containing polymer was obtained. It has been considered that dry etching resistance of monocyclic compounds was insufficient as compared with compounds having polycyclic condensed structure. However the present inventors have found that the copolymer which is obtained in the present invention and comprises fluoroolefin and an unsaturated compound (monomer) of aliphatic monocyclic structure has dry etching resistance higher than that of an unsaturated compound having polycyclic condensed structure, for example, norbornene.
Also it was found that transparency in a vacuum ultraviolet region is excellent as compared with the use of norbornene.
Also studies have been made as to introduction of an acid-reactive functional group necessary for a resist, and as a result, it was found that in addition to the fluoroolefin and unsaturated compound (monomer) of aliphatic monocyclic structure, a specific ethylenic monomer having an acid-reactive functional group has good copolymerizability, which made it possible to introduce an acid-reactive functional group to a polymer. Further the present inventors have found a fluorine-containing polymer in which an acid-reactive functional group is introduced directly to a monocyclic structure and also a novel unsaturated compound of monocyclic structure having an acid-reactive functional group and partly having fluorine atoms. The copolymer comprising such a novel unsaturated compound of monocyclic structure and a fluoroolefin exhibits excellent dry etching resistance and high transparency when used for a resist.